Process for treating ores



- Patented Oct. 8, 1929 OFFICE RALPH F. MEYER, OI IREEPOBT, PENNSYLVANIA, ASSIGNOR T0 MEYER MINERAL SEPARATION GOMBANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF DELAWARE PROCESS FOR TREATING ORES No Drawing. Application filed April 16,

The invention relates to roasting processes for converting the metallic values in sulfide and oxidized ores and similar metalliferous materials to forms susceptible of ready extraction and recovery, and especially to sulfating and chloridizing roasts; and it relates particularly to ores containing, or admixed with, a metal which in its compounds is capable of existing in two or more stages of oxidation. Such metals are, for example, iron, copper, nickel, manganese, and the like, and for brevi ty of reference they will be referred to in this specification and in the appended claims, as reagent metals.

An object of the invention is to provide a roasting process for use with ores containing or admixed with a reagent metal, in which the ore is roasted alternately under oxidizing and reducing conditions, whereby the greatest possible conversion of the metal values in the ore to forms amenable to subsequent treatment is secured.

Another object is to provide a process of the type referred to in which the ore after initial roasting is sulfated or chloridized at a temperature below the decomposition tempera ture of the sulfate of the reagent metal.

Still another object is to provide a roasting process for ores containing a reagent metal in which the desired conversion is produced by initially roasting the ore and then periodically subjecting it to the action of nascent, reactive sulfur trioxide formed in contact with the ore mass, whereby the metallic content of the ore is substantially completely converted to forms capable of ready extraction.

A further object of the invention is to provide a roasting process of the type referred to in which the compounds of the reagent metals are alternately reduced in assisting in the formation of nascent sulfur trioxide, and then reoxidized to forms capable of producing further quantities of sulfur trioxide, this gas being the effective agent producing the desired result.

It is generally considered, that in sulfating roasting one or more of the metals, iron in the form of sulfide for example, is converted to a sulfate, which upon being heated to its de- 1926. Serial No. 102,572.

composition temperature gives up sulfur trioxide, which is the active sulfating agent, the sulfate being at the same time reduced to an oxide form. In the case of chloridizing roasting, the sulfur trioxide formed in this manner initiates the chloridizing reactions by reacting with a chloride to liberate chlorine. It has also been said that under some conditions the metal is first converted to an oxide. with formation of sulfur dioxide, and that the latter then reacts in some manner with the metal oxide to give sulfur trioxide. Regardless of the actual reactions, the processes as now carried out are often inefficient, because frequently substantial quantities of the metal values remain in an untreatable form, and the present processes are not economically applicable to all types of metalliferous ores. Numerous low grade ores and highly refractory ores are known, for example, whose extraction would be highly desirable, but which do not respond to roasting processes, and which cannot be treated by other processes because the cost would be prohibitive for such ores. Thus although widely' used, the present processes are unsatisfactory, largely because of incomplete metal recoveries and their limited applicability.

I now believe that the incomplete conversion referred to is due to the inability of the reagent metal sulfate (or oxide), once it has assisted in producing sulfur trioxide, to further assist in producing that gas, for the reason that according to prior processes the ore is roasted to convert the active metal largely to sulphate, this compound being then broken down at a higher temperature with liberation of sulfur trioxide, and under the conditions as now practiced, the. reduced metal compound remains in that condition. Thus, once the metal compound has been broken down or reduced to its lower stage of oxidation, it is practically inactive, and in consequence metals which are difficultly sulfated (or chloridized) may not be given sufficient opportunity to react completely, or the sulfur trioxide formed by decomposition of sulfates (or through the action of oxides) may be insufficient.

I have found, and it is upon. this that my invention is predicated, that by roasting an ore containing one or more reagent metals,

as .previously defined, and alternately sub oxidizing atmosphere and to supply oxygen for use with the sulfur dioxide, and in some cases it is desirable to admix the reacting gases with water vapor. The alternate treatment with the two gases can be repeated as often as necessary to produce the desired result.

I now believe that the beneficial results of the new process are dependent upon conversion of the reagent metal by roasting to a form adapted to produce sulfur trioxide in accordance with the theory mentioned for prior processes, but whereas in prior processes once the compound has assisted in forming sulfur trioxide it is subsequently practically inactive, according to my process it is cyclically reoxidized, or reviviiied to its active form, whereby it is capable of being used as many times as necessary to.,,cause conversion of sulfur dioxide to sulfur trioxide and thus to insure substantially complete production of readily treatable forms of the metal values and consequent high recoveries.v

The invention is applicable to oxidized or sulfide ores of the type now treated by roasting processes, containing gold, silver, lead, nickel, manganese, copper, cobalt, bismuth, zinc, cadmium, iron, and similar heavy metals, and it is also applicable not only to refractory and low grade ores, containing precious metals, which have not heretofore been amenable to roasting treatments, but also to ore concentrates, and generally to metalliferous substances containing heavy or precious metals, the only condition being that the ore or other material shall contain one or more metals which are capable in their compounds of existing in at least two stages of oxidation (reagent metals).

7 In the case of sulfur-containing ores, the preferred practice of the invention is to roast the material sufficiently to convert all or a portion of the reagent metal to its higher oxidized form, sulfur dioxide being formed at the same time, and then the roasting is continued while air, or air and water vapor, is passed over the ore mass to insure that the reagent metal is in its higher oxidized form, after which it is subjected to an atmosphere of air and sulfur dioxide, or air, water vapor and surfur dioxide, whereupon the sulfur dioxide is almost completely converted to sulfurtrioxide which reacts with the other metals to sulfate them, or with chloridizing agents to set free chlorine, which attacks the metals to form chlorides. I now believe that in the formation of sulfur trioxide --the reagent metal is reduced to a lower oxidized form, and

when in that form it does not appreciably cause production of sulfur trioxide, nor is it appreciably reoxidized in the presence of much sulfur dioxide. However, by repeating the gas treatments, the beneficial results according to the invention are obtained.

The process can-also be applied to oxidized or sulfur-free materials, in which case the material 'is heated and subjected to the gas treatments in the manner described, with equally satisfactory results. In this case sulfur dioxide is, of course, supplied from an outside source. 1

In'either case, lower reaction temperatures are required than are necessary in prior processes, where the'temperature used was necessarily in excess of the decomposition temperature of the metal sulfate, and considerable advantages attend this use of lower tempertures. In the preferred embodiment of the invention, the ore mass during the gas treatments is maintained at a temperature below that of decomposition of the reagent metal sulfate. For example, where the ore contains iron, a suitable temperature will generally be from about 350 to 525 (1., and preferably about 430 0., and in case the predominant reagent metal is cop er, the

upper temperature limit is about 10 C.

Where the reagent metal is other than'iron ,or copper, the preferred temperature will likewise be somewhat below the decomposition temperature of its sulfate, these temperatures being within the knowledge of those skilled in this art.

The process described is fully satisfactory for sulfating, and when applied to metalliferous substances which can be sulfated, higher yields are obtainable than by prior processes. Some ores however, contain refractory c0mbinations of sulfides, tellurides, selenides and the like, which are not readily amenable to sulfating. In such cases, highly satisfactory results are obtained by mixing a halide salt with the ore, sodium chloride being preferred for this purpose. In case sodium chloride is used, the sulfur trioxide apparently reacts with it to liberate nascent chlorine, which is an energetic reagent, attaching the refractory compounds, gold, silver, etc. It will in general be desirable to use the chloridizing process just described, and when applied, the preferred procedure is to add the sodium chloride or other halide gradually to the ore mass as it is subjected to the gas treatments. The presence of substantial amounts of water vapor in the reacting gases assists the process just described.

In oneset of expE'im-ents, copper concentratcs containing percent of copper, 10 ounces of silver and 0.5 ounces of old tothe ton, the balance being iron. sulli des, silica and small amounts of zinc, manganese, etc., were ground and roasted one hour at a temperature of 350 to 450 C., converting a part of the iron=sulfide to oxide and sulfate. The ore was then mixed with 12 per cent. of common salt and treated for 20 minutes at a temperature of 435. C. with anatmosphcre of sulfur dioxide, air and water vapor, and then for minutes with air containing water vapor, and this alternate gassing was repeated twice more, making three hours of treatment in all. The ore was gently stirred during the gas treatments. The final oxidizing treatment produced the maximum conversion of iron to ferric oxide and ferric sulfate. leached with a saturated aqueous solution of chlorine, to oxidize salts in the -ous condition to the -ic state, thus preventing reduction of the noble metal chlorides. Pure water was then used to leach out the soluble salts, and the leaching solution contained more than 96 per cent of the copper and gold, some of the iron and practically all of the zinc. The silver remained in the pulp, and upon leaching ammonium carbonate solution, more than 98 per cent was recovered.

An ore containing about 20 per cent of zinc, 15 per cent of lead, 5 per cent of copper,,

2 per cent of iron, and 550 ounces of silver per ton, together with sulfur, arsenic and small amounts of other metals, was roasted as before, after which 15 per cent of salt was added, and the mass sub ected to gas treatments as before. for a period of 4 hours, the sulfur dioxide, air and water vapor being passed over it for 15 minute intervals, and the air-water vapor mixture for forty minute periods. The thus-treated ore was leached with water, whereby 98 per cent of the zinc and substantially all of the copper was recovered, and 95 per cent of the silver was recovered by leaching the pulp residue with ammonia carbonate solution.

The foregoing examples refer to treatments carried out in mufile furnaces, and the high recoveries of the metals in the ore show its value. The process can be carried out in any suitable roasting furnace, but it is preferred to use a mufiie type multiple hearth furnace, especially one of the wedge type, using a down draft. In using such a furnace, a suitable amount of ore can be placed on the upper hearths and roasted at a temperature of 300 to 450 0., to burn out the iron and other easily roasted sulfides. I The ore then moves to the next hearth, air being down-drafted thereover, and after a suitable period of time, a fresh supply of ore is introduced on the top hearths and roasted, the sulfur dioxide and air being passed down over the first portions.

After cooling, the roast mass was This procedure is then repeated at will, the roasted ore as it moves 'down being alternately treated with air alone and then with sulfur dioxide and air. I

However,.a more suitable procedure is to continuously supply ore to the top hearths of hearths continuously present the atmospheres necessary for the periodic sulfur trioxide formation and the reoxidation of the reagent metal compound, and the process becomes a highly eflicient, continuous one.

In either case, where it is desired to chloridize the ores, common salt may be mixed with the raw ore, but as mentioned previously, it is preferable to add it gradually in regulated amounts, for example, in the last case to the fourth, sixth, etc. hearths. Where wzitervapor is used with the gases, the air used may be saturated with water vapor in any suitable or desired manner. -Where oxidized ores, or sulfur-free ores are treated in multiple hearth furnaces, they may be heated in any suitable manner and the necessary sulfur dioxide-supplied from a sulfur burner, an ordinary roasting furnace, or the like, with fully satisfactory results. Q

The waste gases from the furnace may, and commonly do, contain valuable constituents, such as chlorine, sulfur trioxide, etc. Where orescontaining precious metals are to be leached subsequent to treatment, by the chlorine water method referred to, a suitable chlorine solution can be made by passing.

the chlorine-containing gases through water; and the sulfur gases can be converted tosulfuric acid or recovered in other ways.

Since a number of metals can act like iron as the reagent metals, most ores will contain suflicient of one of them to be fully responsive to the treatment, but in the case of ores not containing sufficient reagent metal, the valuable results can be obtained by intimately mixing with the ore a reagent metal, iron pyrites for example. In the appended claims the term ores is to be understood as comprising ore concentrates, or other metal-bearing materials adapted to treatment by this process.

I claim:

1. A process of recovering metals from their ores comprising roasting an ore containing a reagent metal, and while in a heated state but below the decomposition temperature of the sulfate of the reagent metal subjecting the roasted ore alternately to an oxidizin atmosphere, and then to a reducing'atmospfiere containing sulfur dioxide and oxygen, and subsequently extracting the metal values from the thus-treated ore.

2. A process of' recovering metals from their ores comprising roasting an ore containing a reagent metal, and while in a heated state but below the decomposition temperature of the sulfate of the reagent metal, subjecting the roasted ore alternately to air, and then to an atmosphere of air and sulfur dioxide, and subsequently recovering the metal values from the thus-treated ore.

3. A process of recovering metals from their ores according to claim 1, in which the reacting gases are admixed with substantial amounts of water vapor.

4. A process of recovering metals from their ores comprising roasting an ore containing a reagent metal, and while maintaining the roasted material at an elevated temperature but below the decomposition temperature of the sulfate of the reagent metal, treating it alternately with an oxidizing atmosphere substantially free from sulfur dioxide, and then with an atmosphere containing oxygen and sulfur dioxide, and subsequently extracting the metal values from the thus-roasted ore.

5. A process of recovering metals from their ores comprising roasting an ore containing a reagent metal, and while maintaining the roast body at an elevated temperature but below the decompositiontemperature of the sulfate of the reagent metal subjecting it alternately to an atmosphere containing air and water vapor and then to an atmosphere of air, water vapor and sulfur dioxide, repeating said alternate treatments a plurality of times, and subsequently extracting the metal values metallifcrous materials, the step comprising heating the material containing a metal capa-' ble in its compounds of existing in two stages of oxidation and whose sulphate decomposes in the vicinity of 450 0., to a temperature less than about 450 C. and while thus heated alternately subjecting it to an atmosphere of air and water vapor, and then to an atmosphere containing air, water vapor and sulfur dioxide.

8. A continuous process of treating ores ac cording to claim 2, in which a halide is admixed with the ore.

9. A process of chloridizing metals contained in their ores comprising roasting an ore containing a reagent metal, and while maintaining the roast body at an elevated temperature but below the decomposition temperature of the sulfate of thereagent metal subjecting it to a plurality of alternate treatments with air and water vapor, and with air, water vapor and sulfur dioxide, and during these treatments gradually adding sodium chloride to the ore mass.

10. A process of treating ores according to claim 9 in which the roasted ore during the gas treatments is maintained at an elevated temperature but not exceeding about 450 C.

11. A process according to claim 9, in which the thus-treated ore is leached with an aqueous solution of chlorine, and then with water.

12. The continuous process of recovering metals from their ores comprising continuously roasting an ore containing a reagent metal, advancing the roasted ore progressively while maintaining it at an elevated temperature but below the decomposition temperature of the sulfate of the reagent metal,

adding sodium chloride progressively as the roast body advances, subjecting the progressing ore alternately to air and water vapor,

and to air, water vapor and sulfur dioxide,

and subsequently extracting the metal values from the thus-treated ore.

RALPH F. MEYER.

DISOLAI MEIR 1,730,584.Ralph F. Meyer, Freeport, Pa. PROCESS FOR TREATING ORES. Patent dated October 8, 1929. Disclaimer filed April 9, 1931, by the assignee, 111 (g cr- Mineral Separation Company. Hereby disclaims any interpretation of each claim in said specificationthat would include temperatures below substantially 300 (cl. during the alternating gas treatmm'it specified.

[Ofiiaial Gazette April 28, 1931.] 

